​How do i launch my app without user data?

My friend and I are developing an app that uses a heatmap to show in real-time how busy or quiet certain locations are.

At the initial stage, we are collecting open data from city sources, but unfortunately, most of the useful data is private and not publicly available. For the app to function accurately, we rely on users submitting reports and sharing data through the app. The more people contribute, the better and more reliable the real-time information becomes.

Our challenge is launching the app: in the very beginning, there will be very little real-time data available for new users, which might lead them to lose interest and uninstall the app quickly. Does anyone have suggestions on how we can overcome this and create momentum at launch, so that early users stay engaged despite the initial limited data?